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Sansui QRX5500 receiver

Discussion in 'Electronic Repair' started by [email protected], Sep 18, 2007.

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  1. Guest

    Hi
    This is my own personal receiver. It isa really nice mid 70's unit
    that unfortunately has one channel of the four running really weak.
    The factory schematic for this unit is by far the worst I've ever run
    across and totally useless. Does anyone have any experience with this
    model or do you know of a more appropriate News group to ask technical
    questions of? Thanks very much. Lenny Stein, Barlen Electronics
     
  2. David Farber

    David Farber Guest

    Hi Lenny,

    I have a schematic on fiche and while it's not the easiest thing to follow,
    we could probably figure out what's wrong. Do you have good signal coming
    into the driver board? Also, it looks like each channel has two 3.5A supply
    fuses. Let me know what you've found out so far.
     
  3. Guest

    I have a service manual with a schematic too but its a nightmare to
    try to follow. None of the sub assemblies are connected together and
    the points are so out of focus and illegible that its impossible to
    trace or put the blocks together. Also because its 4 channel SQ, I'm
    not exqctly sure what everything does. Maybe you have a better
    schematic than do perhaps. A conventional schematic where everything
    is connected together so that you could at least follow a signal path.
    That would help so much. The wiring goes through switches, tone
    controls over and under boards, etc. There are four audio paths of
    different colors. I have determined that the problem is in the yellow
    wiring but that is as far as I've gotten. Following it is another
    story though. Lenny.
     
  4. David Farber

    David Farber Guest

    I took a closer look at the schematic. You are certainly correct. If you
    have to trace signal from board to board, it's a nightmare.

    It might be easier to trace back from the speaker output using a tone into
    the 2 channel tape monitor input. Is the signal distorted without a load? Is
    there a signal to the input of the driver board? My schematic indicates the
    signal comes into the F-1482 driver board at C01, C02, C03, C04 depending on
    which channel you're looking at. Those capacitors are 3.3uF at 50V. How does
    the signal look at the volume control? Is the distorted channel in the front
    or the rear?
     
  5. Guest

    First of all thanks for even getting involved in this headache. I
    really do appreciate it. I'm looking at my poor excuse for a schematic
    now. I believe that the driver and outputs are OK. because there is
    output from that channel when different modes are selected. The
    problem is that when you go to four channel synthesized the second two
    channels (left and right rear ) are supposed to be synthesized from
    the two fronts. In two channel with one set of speakers connected to
    the front or main it works fine. But in four channel syn. mode there
    is low output from channel C. the yellow sheilded cables. I'm not sure
    from this schematic what is next in line in the signal path. And the
    volume control is impossible to get at. I could locate ins and outs on
    these boards but I don't know how they're interconnected. This is
    truly your basic rats nest. I tried all the inputs including the
    tuner. They all have this problem. So it is common to everything but
    that doesn't help much. Lenny.
     
  6. David Farber

    David Farber Guest

    Hi Lenny,

    I have a few more questions about what's working so far. Do the rear
    channels operate ok when you're not using synthesized mode? Do the rear
    channels even operate in normal mode?

    My microfiche schematic is in black and white so if you mention colors, it
    won't mean anything to me.

    Here's my interpretation of the signal path when the surround function
    switch is in the "QS SYNTHESIZER HALL" mode and the source is the tape 2-ch
    monitor:

    From the 2-ch tape monitor inputs, it goes through the surround function
    switch, S702, and then into the F2048 board, pin 19 and pin 14. One of
    course is left, the other is right. The output of this board is at the
    collectors of Q12 and Q16. That would be a good test point to check signal.

    I cannot seem to find the connection between the preamp output and the input
    to the driver board which is labeled, "9P6," and "9P8" It appears that this
    goes to a 9 pin "remote control terminal" and terminates there. The F-1484
    board seems to be the likely candidate for the preamp output. If you can
    figure this part out, I think we can piece the signal together from
    beginning to end.
     
  7. Guest

    I'm going to try to follow your signal analysis and hopefully get some
    more infor mation on this set. I'll try to put some more time into it
    next week, after I do the paying jobs of course...I'll let you know.
    Thanks, Lenny.
     
  8. Ken

    Ken Guest

    I have a later model, the 9001, and the main problem is the mechanical
    switches. Many of them are multi pole push switches and I have no idea
    how to clean the conatcts. Otherwise the electronics seem to be OK. This
    was the last of the line, with IC's for all the Quad mode. Ken
     
  9. Guest

    Hi all I'm new here and hope this makes it to all of you, Lenny, David
    and Ken. Just seen everybody's talk on the QRX5500. I think I have
    the same problem, in short when the function switch is in any of the
    QS or phase matrix positions the output levels drop way down. I found
    something awhile back that said if the voltage reg CCA F-1483 voltage
    is not set in its range of 25 V +/- .25V ? then the QS CCA boards will
    not function properly. Mine will not adj more then 18.5 volts and I
    have not been able to trace the cause down. One way I ck'd the
    regular 4ch outs (w/o QS as part of the issue) 2ch + 2ch is to connect
    an external source to the aux-1 inputs (4 jacks). Either in parallel
    or one at a time. Set the function switch to Discrete and look at
    each Spkr output. Each one should have the same Lvl with all balances
    at middle. If those are fine then this isolates the problem to either
    F-1483 Volt Reg, F-1488 connection interface, or F-2047/2048 QS Syn/
    Vario CCA.

    I am now at a stand still. No parts for V regulator. And no info for
    QS CCA. Like all of you the diagrams suck. I am trying to find how
    CCA are connected. The boards have terminal # on the diagrams but no
    info on where they go (I don't want to trace each wire in ea harness.
     
  10. I have a later model, the 9001, and the main problem is the switches.
    "Seems to be" is the operative term. These units are notorious for bad
    solder connections on the QS logic board.
     
  11. David Farber

    David Farber Guest

    Regarding the 25V output, do you have 44 volts at the emitter of TR04?
    12volts at the emitter of TR05? Did you test the ESR of the caps in this
    circuit? What is the voltage drop across R17, 330 ohms? The schematic for
    this part of the circuit is fairly good even on my microfiche.
     
  12. Guest

    i have that reciever also and my problem is my left channel are
    distorted i clean the knob and dont work...so i connect one speaker to
    the A speaker and one speaker to B speaker channel and i only use the
    two channel and move the know to AB channel....i am not a stereo
    tech...but i work on electronic so i know how to read and use
    meters...any advice ??
    left channel are distorted like a bad reception...even i play cd...
     
  13. David Farber

    David Farber Guest

    Repairing a receiver with distortion is not a beginner's project. On a set
    this old and complex, it will be a challenge even for an experienced stereo
    tech.
     
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